Coded track circuit for railroads



2 Sheets-Sheet 1 ncowtwcou 42.3529 rf; oucdvgooud E vs oLPcoU LoELowmce.

F. X. REES CODED TRACK CIRCUIT FOR RAILROADS Filed 001'.. 16, 1942 lull' lili S5035 ESP Jan. 9, 1945. F x. REES coDED TRACK CIRCUIT FOR RAILnoAns Filed Oct. .16, 1942 2 Sheets-Sheet 2 |Nv NToR ATTOR'NEY Patented Jan. 9, 1945 UNITED STATES; PATENT OFFICE consu/:ration: CIRCUIT Foa RAuRoADs Frank X..Rees, Rochester, N. Y.,V assigner to Gen.

eral Railway Signal Company, Rochester, N. YJ?

Applicationctoben1.6, 1942, SerialyNo.. 462,225

13` Claims.

This .invention relates to codedttrack circuits for railroads, and ,more z particularly f pertains. to

an'. improved mannerf of impressing codedimpulses on a coded track circuit.

Inmyy prior application,Ser, No. 1,453,313; l'ed- August 3, 4194:2,i now PatentNo. 2,353,930, grantedf July 18,1944; coded@trackfgcircuits aradisclosed in which the energy used -for .the codeimpuls'es is ofthe pulsating 1 type.-A ,y More specifically, alter.- nating current. is used` as. a sourceof energy .with

a half-wave rectierzso Yemployed astoallow only. one polarity ofuthealternatingicurrentwave :to 1 be .impressed duringv a code. impulse on the .trackI a.: circuit.,A This not only provides'.betterxshuntingay sensitivity for the track circuit, but also providesy that train rcontrol .ora cabl fsignal.-v .apparatus can becontrolled bythe .coded trackcircuitimpulses as .well as, wayside signals.. No claim .to .this fea-.2..

ture is made. in: this application The object of the presentinventionis ;to'pro.

vide improved meansxo'fvapplying.coded in'lpulsesr` of this pulsatingcurrent;l toithe trackcircuit so:`

as to avoid eithermakinglor openingthescontrol contact for.;such..pulsatingtrack circuit current while currentis .actuallyflowing It is, ofcourse,

well known. that when contacts open a .circuit in which current isfiowing, randare occur'ssinv accordance `with thev potential. of. the energy; butV n it should a1so,;becappreciatedthat when contacts close, thereis a .certainamountwof bounce; ofthegmovable contactslifwhich lcauses miniature.)A arcs to be made;` .Theseirniniature arcswould'lcetv of -relativelysmall importance in theusualcomv trol circuits,;but-,:in;.;coded.track .circuits where the contacts are` `being .opened and. :closed y .subfA stantially continuously, these .miniature arcs tend. to `pit the .contacts and otherwisedeformtthe contacting surface. inasmuch asiit is desirable that.; these coding;` contacts last zover. a long period off.

time, it is desirable .to arrange. the apparatus and circuit sofas to minimize the. arcingatthe code'u transmitting contacts; xThlsisespeciaHy desirable when a train is in a track circuit shuntinga.y

the railsastthe current .suppliedtozthe track through thegcoding ycontact'is ata maximumunder such circumstances,fandtis of a very sub-hy stantial value. n

The present invention:.=.proposestoreduce the arcing or sparkingoffthecoding contacts byde-.f termining that thesecontactszshall actually opent.

and close ,onlyfwhil'eitherefis tno Acurrent yflow d through such. contacts; and. this `is accomplished in accordance with. thepresent inventioniby apr plying .energy tozthei.1code;transmitting relayr at v f propertimes so that itscodingcontacts will shift, only while-there is;no.-.current flowing ,throughY them. This ycanrbe` .accomplished lbecause the pulsating vcurrent has-periods -Whenyno` current. flows ythrough. the codedwtrack; circuit ,'.inclu :lingr4v the coding contacts..;.

Other objects, lpurposesfand,characteristic fea..y tures.ofgthe=present..invention will be in -part obviousl from the accompanying drawingsand in partfpointed out as the `description ofthe inven-1 vtiontprogresses.-

Indescribingrthe invention in detail, reference will .be made tov the ,accompanying drawings, yin which:` n

Fig.. 1 showsastretch ofnsingle track d1-` videdintotrackv sections,.each track section ccm;.

prisinga track circuit betweenisuccessive signal locations ina coded .trackV circuit'. signalling sys.

tem; and

Fig; '.2 shows ,a .diagram ofcertain operating ,,relationshipsappertaining; to 1 the .embodiment of. f

the .present invention..

With reference. to Fig, 1, .a track section T is shown'extending'.betweenisignal locationsz and f. 3. Each offthese;.signals are,v assumedto be `ofw- ,1 the colory .light/type..` having .upper .f and lower arm signal. mechanismssuch ,as signal .mechanism 2A. and2B` forthe .signal y2. Although each of these signal mechanisms is assumed-tobeofthe multiple ,aspectftype` as -,.shown-, for example, in the priorpatent v.to,O..S.;1ield, PatentNo. 1,835,150, 1 dated December 8, 1931, it should be understood thatany suitable mechanismlmaybe employed.:` and that; any desiredtype signal may heused` in place` of the type, shown,v

Thejupper andlower armsof .each signal, such as 3A andSB foruthesignalf,.are controlled to givevv 4 in combination four distinct indications,` namely, redover red indicating stop yellow over v redfindicatingstop;at .the1 nextysignal; yellow` over .yellowyindicatingystopat theisecond signal; and/green overrgreen indicating.,proceed. All of this has beenqdescribed Vin detail in my. above mentioned.v pricryPatentNo.7 2,353,930.v Itis believed ,to beqsufiicientJforan understanding of: the-present'inventionl to knowthat when the sigy l nal f3 yindicates, redy overrred or stop all of ,its associated signal` repeating relays 3AGYP, SBGYE and ,SHRai-,ef deenergized. When the signale gives any .lessrestrictive indication, the ,relay 3HE ispickedlzlp; ibut. if such less .restrictive indicationfis vyellow `overfredfthen the relay SAGYP. is 'picked up lwhileIthe .relay 3BGYP ref mains. ,deenergizedr and if ,the .indication is yel-r low'over yellow. thenboth;;of; the relays SAG-YB and BBGYP arepicked; up. t

Itwillbe seen.'fromfplig-y 1 of-the drawings, that-the`left-hand-- .end of; the track circuit Tis provided with-.a track relay 2IRxconnected across the .track =circuit;having .finrmultiple therewith. .a `bleederresistor 5 landain.: series therewith a variable resistor. 6.f,.This;track relay yZTR is of the polarized/type fhaving its polar contacts biased,toyonevposton. sothatit is actuated toA an:l 4 ipposite, position only/upon the .reception of -polarfismpulsespfa particularspolarity.`

EFBP includes front contact 8 of relay ZFP.

These relays 2P? and ZFBP are thus continuously energized whenever the track relay 2TR is receiving code over the track section T, but if the track relay ZTR is continuously deenergized then both of these relays are dropped away, In

.such a case, the relay ZFP drops away rst followed by the dropping of the relay ZFBP upon the opening of front contact 8. If, on the other hand, the track circuit including the track section T should become erroneously energized with steady energy of the proper polarity to maintain the polar contacts of the track relay ZTR in actuated position, the relay ZFBP would drop away although the relay 2F? would remain picked up, In either case, it would be apparent that the relay ZHR would not receive energy because of the open condition of the front contact 9 of the relay ZFBP.

While the track relay ZTR is responding to any code, its operations are repeated by a two-position polarized relay ZTP which has polar contact I9 biased to a normal position. This repeating relay ETP is controlled by polar contact II through a circuit including front contact I2 of relay ZFP, as shown in my above mentioned Patent No. 2,353,930, but, if desired, the Decoder apparatus may be directly controlled by contact il without the repeater relay 2TP.

When the track repeating relay ZTP is operated in accordance with the reception oi' a code by the track relay ETR having 'T5 impulses per minute, the decoding apparatus is not effective to energize the relays ZBHR and 2DR, but the relay EHR is maintained energized. This would cause the signal 2 to display the aspect of yellow over red. On the other hand, if the track repeating relay ETP is being actuated with code impulses at the 120 rate, then the relay ZBHR is caused to be energized by the decoder apparatus while the relay 2DR remains deenergized. It is of course understood that the relay l2ER is picked up by impulses of any code rate being received. Thus, the signal 2 is caused to display a yellow over yellow aspect. When the 180 code rate is received by the track repeating relay ZTP, then the decoder apparatus causes the relay 2DR to be picked up while the relay ZBHR is deenergized. This relay 2DR in combination with the relay EHR causes the signal 2 to display a green over green aspect. It is to be understood that the nature of the -decoding apparatus and the control oi the signal mechanisms 2A and 2B of the signal 2 is immaterial to the present invention and therefore have not been shown in detail, but reference may be made to my above mentioned application for all such details desired.

At the transmitting end of the track circuit, a track transformer TF has its primary winding supplied with alternating current energy and its secondary winding is connected across the track section T in series with a rectier unit I3, a variable resistor I4, with polar contact I of the transmitter relay CTP in an actuated position. A multiple bleeder resistance I6 is connected across the track circuit. It is thus seen that Lil half-Wave alternating current pulses are applied to the track circuit when the front contact I5 of relay CTP is closed.

The transmitter relay CTP is of the staywhere-put magnetic stick type relay, that is, its polar contacts are operated to the right or to the left in accordance with the polarity of energy applied to this relay, and its contacts remain in the positions to which they are last operated.

The transmitter relay CTP is controlled by a neutral transmitter relay CT by energy supplied from the secondary winding of a peaker transformer PTF. This neutral transmitting relay CT is controlled through contacts I1, I8 and I9 in accordance with the indications of signal 3 subject of course to traffic conditions in advance of that signal. Thus, the relay CT may be operated in accordance with a. l5 code rate, a 120 code rate, or a code rate as supplied by the coding contacts 15C, IZIJC and I80C respectively depending upon the particular trafhc conditions then existing. The particular structure of the coding contacts 15C, I2IlC and IBUC is believed to be immaterial to the present invention and has not been shown in detail, it being assumed that these contacts may be operated continuously for the purposes of the present disclosure, although such coding devices might be set into operation only as required by suitable approach control.

The peaker transformer PTF has been diagrammatically illustrated as having a primary winding connected to an alternating current supply. Its secondary winding is provided with a. mid-tap connected to one side of the transmitting relay CPT. The outer terminals of this secondary winding of the peaker transformer are respectively connected through rectifier units 2| and 22 as selected by the position of contact 20 of the relay CT to the other terminal of the transmitter relay CTP. This peaker transformer PTF is for the purpose of changing the usual alternating current sine wave to an abrupt or peaked wave form, as more completely described in my prior Patent No. 2,123,965, dated July 19, 1938. This peaked type of wave form has also been shown in the diagram of the accompanying Fig. 2. Inasmuch as the primary Winding of both of the transformers TF and PTF are connected to the same alternating current supply, the voltages of their respective secondary windings are in time phase. 1n the diagram of Fig. 2 the Wave forms are assumed to be voltage wave forms, although they could also be assumed to be current wave forms, as the inductive characteristics of the circuits have been neglected for the sake of simplicity in the presl ent discussion.

For the purpose of the present disclosure it is assumed that the alternating current supply to the primary windings of these transformers TF and PTF is of the usual 60 cycle current commercial supply, although it should be understood that any other suitable frequency might be employed. Inasmuch as the coding contacts 15C. I2IJC and IBUC are operated by oscillator mechanisms wholly independent from the character oi' alternating current supply, the opening and closing of the contact 20 of the transmitter relay CT will bear no particular relation to the current flow in the peaker transformer PTF. However, it is assumed that the contact 20 is shifted in accordance with the particular code rate then selected and when it closes either front or back points, the next positive half-wave of current supplied rby the secondary of the peaker translformer PTF vows through the particular recti-4 fier unit in the circuit then closed by contact 20 in a direction toY act upon the transmitter relay CT-P to cause it to shift its contacts to the opposite position.

More specifically, let us assume thatthe upper end of vthe secondary winding of the Apeaker transformer PTF is .the positive terminal with respect to the `center-tap, then current will flow through the rectier .unit 2I and the transmitter relay CTP when vfront contact 20 is closed. only during the positive half of each alternating current .cycle. Similarly, let us assume that the center-tap of the secondary of transformer PTF is positive with respect to the lower terminal, then current will flow through the rectifer unit 22 and the transmitter relay CTP in an opposite direction when back contact 23 is closed but only during the positive half of each alternating current cycle. Thus, during the positive half-wave of any alternating current cycle, the relay CTP can be shifted to either its right or left-hand position, dependent upon whether the contact 2i) of the relay CT is closed in a front or a back point position. On the other hand, -it is seen that regardlessof the position `of contact 20 of relay CT, no current can flow through the relay CTP during the negative-halfwave of any alternating current cycle due to the .rectifier units 2I and 22.

yAlthough the rectifier unit I3 is connected in its circuit to permit the positive half-waves of alternating current from the secondary of the transformer TF to flow to the track rails when contact I5 is closed, the shifting of the contact |15 of relay CTP in response to a positive halfwave does not actually occur until that positive half-wave has ceased and the negative halfwave period is present. This is indicated in Fig. 2 by showing that the relay CTP may have its circuit closed .by contact 20 at or before the wave front of the peaked positive wave from the secondary winding of the peaker transformer PTF, 'but it does not shift its contacts until some time during the succeeding negative half-wave period due to the electrical ,impedance of the relay and the inertia of its armature and contact struc ture. This operating' time of relay CTP is indicated in the drawing of Fig. 2 by an arrow with suitable legend. The optimum time at whichthe contacts of the relay CTPr should shift is assumed to rbe at the median of the negative half-wave, but it is of course understood that such contacts may shift any time during such negative half-wave and there will be no current flow through the coding contact I5 and the track circuit by reason of the rectifier unit I3. This is indicated in Fig. 2 by the arrow having the legend margin of operation for relay CTP, which arrow is adjacent the curves for the voltage ofthe secondary of transformer TF.

It should be noted in this connection, however, that'the current is assumed to be in phase with 'the voltage, and if such current is not in phase with the voltage then the margin of operation for the relay CTP shifts `relative to the voltage wave indicated in Fig. 2. But inasmuch as the vrelay `response is ydependent upon the current in its circuit, and so long as the current phase displacement i`s substantially the same in the cir- -cuit for relay CTP as in the track circuit, the

phase displacement of such current is immaterial 'to a consideration of the operation of the circuit arrangement 'thus provided.

From the above, it will be understood that the .relay CTP may be operated to either position in .half-wave of alternating current flowing through its circuit following the shift of the contact 20.

Then due to the time lag of the contacts of the relay CTP, its contact I5 will not shift (either open-or close) until the following negative half- Wave 4of the alternating current at which time there is actually no current flow through such contact I5 dueto the rectifier unit I3. Obviously, ifthere is no current ow through contact I5 when it shifts to an opposite position, there is no current to be broken and no arcing can occur. Itshould ybe understood that the relay CTP not only receives energy from the first positive half- Wave of alternating current following the shift of the contact 20, but also receives the successive positive half-waves of alternating current in the direction then .established until the contact 20 is again shifted to a new position at which time the positive half-waves of alternating current are passed through the relay CTP in the opposite direction. Likewise, it should be understood, that throughout `the time that the contact I5 of the relay CTP is in its left-hand position, positive half-waves of alternating current are applied 'toythe track circuit T. In other words, the coding contacts such as C, I20C and ISOC open and close at regular intervals and depending upon the particular coding contacts then selected by the trafficI controlled relays SAGYP, 3BGYP and SHR, the contact I5 of relay CTP is opened and closed at the same regular intervals as the coding contacts .then selected. During each period of the closed condition of contact I 5, a succession of positive half-waves of alternating current are applied to the. track circuit T to comprise the on period of the code. Thus, the contact I5 may be operated in accordance with the coding contacts at any selected rate and apply code pulses yto the track circuit each comprising a series of alternating current half -waves. l

It is of' course understood that the alternating' current supply may be of any suitable frequency, but it may happen that if a sufficiently high frequency is selected, the relay CTP will not receive sufficient energy during any one ,half-wave of alternating current to actuate its contacts within the time period indicated in Fig. 2. In such a case, it may be desirable to change the relationships between the rectifier I3 and the rectiers l2I and 22 so as to energize the relay CTP during a negative half-cycle while current is not flowing through itscontact I5 and then regulate the time response of the relay CTP accordingly so that the contact I5 will not respond to shift its contacts until a later negative half-cycle while current is not flowing through the rectifier I3 and contact I5. It will thus be appreciated that certain variations in the characteristics of the apparatus may be provided for in practice in order to accomplish the purposes and features of the present invention, and all such variations are of course assumed to be within the scope of the present invention.

Although in accordance with the present invention, it is desirable to employ a peaker transformer, so as to accentuate the effect of an alternating current half-wave upon the transmitter relay CTP, and so as to be able to mo-re accurately determine the time at which the relay contacts Will actually shift, it `should be understood that the use of a peaker transformer is not absolutely essential to the practice of the invention. In other Words, the invention should be considered suiiiciently broad to include the use of usual transformer in the organization as shown in Fig. 1 in place of the peaker transformer PTF.

Thus, a coded track circuit has been provided for controlling wayside signals by coded impulses of pulsating current that will also govern train control or cab signalling apparatus, and these pulses of coded energy are impressed upon the track circuit of such a system in a manner to prevent arcing at the code applying contacts and thereby provides a more reliable system operable over a considerably longer period of time than the usual systems now known.

Having described the circuits and apparatus for applying impulses to a coded track circuit signalling system as one specic embodiment of the present invention, it is desired to be understood that this form is selected merely to facilitate in the disclosure of the invention rather than to limit the number oi forms which it may assume; and it is to ce further understood that various modifications, adaptations and alterations may be made to the specific form shown to meet the requirements of practice without in any manner departing from the spirit or scope of the invention except as limited by the appended claims.

What I claim is:

i. In a coded track circuit for railroads, a section of track having code receiving means connected to it at one end, and code transmitting means at the other end comprising a source of alternating current, a half-wave rectifier, electroresponsive contact means for connecting and disconnecting said source and said rectifier in series across said track rails, and circuit means for at times causing said electro-responsive contact means to make said connection and to at other times break said connection, said circuit means being connected to said source and responsive only to particular half-cycles of said alternating current so as to cause said electroresponsive contact means to make or break said. connection only when alternating current is blocked by said half-wave rectiiier.

2. In a coded track circuit for railroads, a section or" railway track having code receiving means. connected across the rails at one end, and codetransmitting means associated withv the othery end of the section comprising a source of alternating current, a half-wave rectier, contact means for connecting said source and said rectifier in series across said track rails to apply half-- cycles of a particular polarity to said rails, and, circuit means for periodically causing said contact means to be effective to establish said connection, said means being actuated by alternating current from said source in a manner to initially effect such connection only during halfcycles oi' alternating current from said source which are not passed by said half-wave recti- Iier.

3. In a coded track circuit, an insulated tracki section of railroad track, a source of alternating current, a half-wave rectier, coding contacts and a transmitting relay associated with one end of said track section, circuitJ means causing said coding contacts to operate said transmitting relay to its opposite positions at selected rates substantially lower than the rate of said alternating current, said circuit means initially operating said. relay to one position or the other only during a negative half-wave of said alternating current,

' circuit means controlled by said transmitting relay in one position for connecting said alternating current source and said half-wave rectier in series across the rails oi said track section to apply positive half-waves of alternating current, whereby said connection and disconnection of said alternating current to said rails is effected only during the absence of current flow to such rails, and code receiving means at the opposite end of said track section connected across the rails thereof and distinctively responding to the code impulses each comprising a series of positive half-waves of alternating current.

4. In a coded track circuit for railroads, an insulated section of railroad track having code receiving means connected at one end, and code transmitting means associated with the other end comprising, a source of alternating current, a half-wave rectiiier, a transmitting relay of the two-position polarized type acting when in one position to connect said source of current in series with said rectier across the rails of track section, coding contacts operated at predetermined selected rates, and circuit means including a peaker transformer and rectiiier means for causing said transmitting relay to be periodically operated to its two positions alternately in accordance with the operation of -said coding contacts, such circuit means causing said transmitting relay to be initially operated to a new position only during a half-cycle of alternating current during which current is prevented from flowing to the rails of said track section from said alternating current source by said half-wave rectiiier.

5. In a coded track circuit for railroads, a. section of track the rails of which have a code receiving means connected across one end and code transmitting mea-ns connected across the other, said code transmitting means comprising a source of alternating current, a half-wave rectifier unit, a transmitting relay of the magnetic-stick type acting when in one position to connect said source of current in series with said rectifier unit across the rails of said track section, a peaker transformer having a primary winding energized from said source and having a secondary winding with a mid-tap connected to one terminal of said magnetic-stick relay, circuit means connecting the other terminal of said magnetic-stick relay to the opposite terminals of said secondary winding through oppositely poled rectifier units at different selected rates in accordance with predetermined codes, to thereby cause said transmitter relay to initially shift its contacts to new positions only while current iiow to the rails of said track section is prevented by said half-wave rectiiier unit.

6. In a coded track circuit for railroads, a track section, means including a code applying circuit for applying code impulses to one end of said track section each impulse comprising a succession of half-cycles of alternating current of one relative polarity, said means acting in such a way as to make or break the code applying circuit only during the absence of such half-cycles of alternating current, and code receiving means at the other end of said track section responsive to the code impulses received over the rails oi such section for controlling the indications of a traiiic governing signal.

7. In a coded track circuit for railroads, a section of railway track having a signal at the entrance thereof for' governing traflic into such section, code transmitting means at the exit end of said section comprising a source of alternating ,s current, a half-wave rectier, means connecting and disconnecting said source and said rectier in series across said track section at regular intervals at a selected rate, said means performing such connecting and disconnecting function only during the half-wave of any alternating current cycle during which said rectier will not pass current, and code receiving means at the entrance end of said section responsive to the half-cycles of alternating current received over the track rails at the intervals of the selected rate for controlling the indications of said trailic goveming signal.

8. In a coded track circuit for railroads, a section of railway track having code receiving means connected across the rails at one end, and code transmitting means associated with the other end of the section comprising a source of alternating current, a half-wave rectifier, contact means capable of being rendered effective to connect said source and said rectier in series across said rails, coding contacts operating at different predetermined code periods, and circuit means controlled by said coding contacts with alternating current energy from said source for rendering said contact means effective during said code periods but being initially rendered eiective for each code period only during that portion of an alternating current cycle during which current is prevented from flowing by said half-wave rectiier, whereby half cycles of alternating current are applied during the successive code periods, and whereby said source and said half-wave rectier are initially connected across the rails for each code period during the absence of current ilow to thereby prevent arcing of said contact means.

9. In a coded track circuit for railroads, a section of railway track having code receiving means connected across the rails at one end, and code transmitting means associated with the other end of the section comprising, a source of alternating current, a half-wave rectier, contact means capable of being rendered effective to connect said source and said rectifier in series across said rails, coding contacts operable at predetermined code rates to measure oil' code impulse periods, a peaker transformer having a primary winding energized from said source and having a secondary winding, and circuit means including rectier means for connecting the secondary of said peaker transformer through said coding contacts for governing said contact means to render such contact means initially eiTective for each impulse period only during that portion of an alternating current cycle during which current is prevented from owing by said half-wave rectier though the rail circuit.

10. In a coded track circuit for railroads, a section of railway track, a source of alternating current, a half-Wave rectifier, coding means including coding contacts operable to measure oit' recurring code periods, a transmitting relay including contacts operable to be effective to connect said source and half-wave rectifier in series across the rails at one end of said track section, circuit means controlled by said coding contacts for at times energizing said transmitting relay from said source to render its contacts effecperiods, said circuit means tive during said code including asymmetric units permitting said transmitting relay to be energized from said source only at a time to cause its contacts to be initially rendered effective or ineffective only during that portion of an alternating current cycle during which current is prevented from flowing to said track section by said half-Wave rectifier, and code receiving means at the opposite ends of said track section connected across the rails thereof and distinctively responding to the energization thereof from said source at said one end of said track section.

11. In a coded track circuit for railroads, a section of railway track having code receiving means connected across the rails at one end, and code transmitting means associated with the other end of the track section comprising, a source of alternating current, a half-wave rectiiier, coding means including coding contacts operable to measure orf code periods? a transmitting relay of the two-position magnetic-stick type having contacts for in one :position connecting said source and said half-wave rectifier in series across the track rails of said section, and circuit means controlled by said coding contacts to energize said transmitting relay in opposite directions alternately from said source only during particular half-cycles of said alternating' current to cause the contacts of said transmitting relay to be actuated to opposite positions only while said half-Wave rectierprevents the ow of current from said source to said track section..

12. In combination, a source of alternating current, a rectier unit of the half-wave type, a load circuit, electro-responsive circuit controlling means for connecting and disconnecting said alternating current source and said rectier unit in series across said load circuit, movable control contacts, asymmetrie circuit means, and circuit means governed by said movable control contacts for `at times connecting said source through said asymmetric circuit means to said electro-responsive circuit controlling means in such a manner as to operate it to cause said connection or disconnection dependent upon the position of said movable control contacts and at a time that current is blocked by said rectier unit of the half-wave type.

13. In a track circuit for railroads, an insulated section of railway track having a track relay connected across the rails at one end and transmitting means associated with the other end of the section comprising, a source of alternating current, a rectifier unit of the half-wave type, electro-responsive contacts operable to one position for connecting said alternating current source and said rectifier unit in series across said tr'ack section-and operable to the opposite position for opening such connection, movable control contacts operable to different positions, asymmetric circuit means, and circuit means for connecting said source through said asymmetric circuit means to said electro-responsive contacts in such a manner as to cause said electroresponsive contacts to be operated to said one position to make said connection or to its opposite position dependent upon the different positions of said movable contacts and to initially cause the operation of said electro-responsive contacts at a time that current is prevented from owing through said rectifier unit of the halfwave type irrespective of the time of the operation of said movable contacts to their different positions.

FRANK X. REES. 

